The advantages of continuous administration of spinal anesthesia have long been appreciated by anesthesiologists. Unlike conventional single-shot techniques, continuous spinal anesthesia (“CSA”) with an indwelling catheter facilitates the administration of anesthesia over an unlimited period of time and furthermore provides the ability to carefully control the level of the block by administering repeated small, incremental doses of anesthetic. As compared to continuous epidural anesthesia, which has become widely used as a substitute for spinal anesthesia, CSA generally requires far smaller quantities of a drug to achieve the desired effect, has a definite endpoint of correct catheter placement, requires no “test dose,” and produces a much more reliable and less spotty block.
Unfortunately, technical problems have severely limited the usefulness of continuous spinal techniques. Until recently, the standard technique of inserting the spinal catheter through the spinal needle, coupled with the difficulty of manufacturing truly small needles and catheters, has meant large needles and catheters were required. This in turn has resulted in an unacceptably high incidence of post-dural puncture headaches (“PDPH”).
In the mid 1980's, various technical advances fueled renewed interest in spinal anesthesia in general, and in CSA in particular. Improvements in manufacturing ever-smaller conventional (QUINCKE™) spinal needles of 25 gauge, 26 gauge, and even 30 gauge have significantly reduced PDPH incidence. These results have allowed for the use of spinal anesthesia in age groups and in procedures which were not previously considered suitable.
At the same time, advances in catheter manufacture have made possible spinal catheters of 28 gauge and 32 gauge which would fit through relatively small spinal needles. Unfortunately, these catheters proved difficult to handle and to make. Moreover, such catheters were expensive, and, more ominously, they were associated with several reports of neurologic damage (i.e., cauda equina syndrome). Many clinicians experimented with these catheters and subsequently abandoned them. These types of catheters were ultimately removed from the market by the Food and Drug Administration (“FDA”).
The FDA's decision to recall and ban the marketing of microspinal catheters for CSA in the U.S., and its requirement that any new device for CSA be subjected to an extremely stringent pre-market approval process, have resulted in a freeze on the development of these products, at least in the United States. Nevertheless, the use of such catheters for injecting local anesthetics for the establishing surgical anesthesia is not the only use to which such devices might beneficially be put. In fact, the injection of narcotics, such as FENTANYL™, for analgesia during labor would be a very desirable use of such catheters.
Installing a conventional catheter generally requires several cumbersome steps involving threading long, very thin catheters through a spinal needle. Simply threading a catheter into the end of a spinal needle can be so difficult that some manufacturers include a “threading aid” as part of their kit. In short, the conventional spinal catheter threading operation requires considerable time and effort on the part of a clinician. Once threaded, a degree of uncertainty exists for the clinician as to how far to insert the catheter. Also, a risk exists that a piece of the catheter might be sheared off by the needle, if the catheter were to be pulled back during the threading operation. In such cases, bits of catheter could potentially be left behind in the intrathecal space. Furthermore, removing the spinal needle, while holding the catheter in position, can be a challenge. Additionally, attaching a hub/injection adapter to the naked end of the 28 gauge or 32 gauge catheter can be even more of a challenge. Finally, once the adapter is successfully attached, the small lumen of the catheter permits only a slow flow of either CSF or anesthetic.
A parallel technical development has been the introduction of non-cutting spinal needles, such as the “Pencil Point” type needles, which have been shown to drastically reduce PDPH incidence. Examples of Pencil Point type needles include the Sprotte and Whitacre non-cutting spinal needles. In terms of PDPH incidence, a 22 gauge Sprotte needle seems to be roughly equivalent to a 25 gauge or 26 gauge Quincke needle, while a 24 gauge Sprotte needle or 25 gauge Whitacre needle essentially eliminates the risk of PDPH.
One problem of Sprotte and Whitacre non-cutting spinal needles is that the injection orifice is on the side of the needle. Failures in spinal anesthesia administration have been known to occur when the needle was “half-in, half-out” of the intrathecal space, i.e. the needle was only partially inserted into the intrathecal space. Another problem with Sprotte and Whitacre spinal needles is that the smooth curved tip profile provides no definitive feedback signal or “click” to the clinician when the dura is punctured. This lack of feedback contributes to uncertainty in catheter tip placement for the clinician.
One proposed solution for overcoming the limitations of the conventional catheters mentioned above and a solution which has been approved by the FDA is a flexible spinal needle, described in U.S. patent application Ser. No. 10/694,235, filed Oct. 27, 2003, (U.S. 2005-0090801 A1, published Apr. 28, 2005) the disclosure of which is incorporated by this reference in its entirety herein. Specifically, this particulate flexible spinal needle may be used for CSA while essentially eliminating the risk of PDPH.